The use of optical fibers for signal transmission, both broadband and narrow band, is more and more becoming the dominant signal transmission mode in communications. The bandwidth characteristics of optical fibers, as well as their relative immunity to certain types of interference and contaminants make them a highly desirable transmission medium in high capacity trunk lines as well as in lower capacity feeder and distribution lines.
Individual optical fibers, regardless of end use, are generally combined in an optical fiber cable which contains a plurality of glass fibers, each of which is protected by at least one layer of a coating material. Generally, the optical fibers are assembled into units which are held together by binder ribbons or tubes to form a cable core. The core is enclosed by either a plastic or a plastic and metallic tube and a plastic jacket. Instead of bunched individual fibers, the core tube may contain optical fiber containing ribbons.
Regardless of the cable composition, it is necessary that lengths of fiber cable be spliced at their ends to corresponding lengths of fiber cable or to other optical fibers, which entails splicing each of the individual fibers in a cable to its corresponding fiber in the adjoining cable. To this end, there is provided a splice closure arrangement, usually comprising a protective case which contains, for example, a splice tray and a plurality of splice holders mounted thereon into which the encased splices are inserted and held. The cables are entrant into the case and generally are clamped at each end of the case to reduce or eliminate the effect of tensile forces on the cables and the splices. It is generally necessary that sufficient amounts of fiber slack be provided within the case, such as, for example, half a meter of fiber length so that the individual fibers can be pulled clear of the closure case for preparation of the ends and for splicing and, also, at least in some cases, to absorb tensile forces. For a multifiber cable there should be, within the closure case, an arrangement for positioning and storing the slack and for keeping the fibers arranged in an orderly manner. Because of the delicate and somewhat brittle nature of the individual glass fibers, they cannot be crimped or bent to too small a radius. Thus, it becomes necessary to provide storage facilities for the slack fiber that minimize fiber bending, at least bending which involves small radius bends. U.S. Pat. Nos. 5,097,529 of Cobb et al.; 4,679,896 of Krafcik et al. and 4,332,435 of Post are illustrative of prior art arrangements addressing the problem of both splice and fiber slack storage.
Typically, prior art splice closures are somewhat complex, difficult to use and to access, and necessarily are bulky. As a consequence, they are not economical when used for splicing relatively low count optical fiber cables, such as, for example, drop cables or CATV applications. Also, when used for low count cables, their bulkiness makes it difficult to provide adequate storage room in cases where small pedestals are used, for example, without sacrificing accessibility. In addition, closure re-entry is more often than not difficult and time consuming. Some prior art closures contain fiber and splice organizers which place higher than desired stresses on the fibers, while others fail to provide adequate storage for the fiber slack. For example, a splice closure may have a central transverse bulkhead to which the fibers and splices are attached, and to which the fibers are directed with a minimum of slack. Such an arrangement can be susceptible to tensile force damage. In other arrangements, all of the fibers are looped within a retainer or the fiber slack is stored on spools. In either case, identification, repair, or splicing is made difficult and attempts to rearrange the fibers can result in too sharp bends causing increased signal attenuation or in possible fiber cracking. In high count cable splicing, these factors are not as important inasmuch as entry into the splice closure is seldom necessary. With low count drop or distribution cables, however, entry to add or remove splices is a frequent occurrence, hence a splice closure which provides both easy entry and ready access to the splices as well as a sufficiency of fiber slack is highly desirable. Thus, in one type of prior art closure, the device has a modular construction comprising a plurality of tray-like members each adapted to retain and store at least one fiber. The trays are stacked on top of each other, and each is hinged separately at one end thereof to a carrier, which allows them to move relative to one another. Such an arrangement is complex and uneconomical for use in low count fiber situations although for high count arrangements, it is adequate.
In U.S. Pat. No. 4,927,227 of Bensel et al., there is shown a splice case arrangement which affords an added measure of protection to the optical fibers involved in the splices. That arrangement has a support member including a base for supporting an optical fiber breakout and a plurality of splice trays. The breakout allows a user to separate fibers into groups before they are routed to one of the trays. In another prior art closure, a tubular cover having a closed end and an open end is adapted to receive and be sealed to a cable termination assembly. The cable termination assembly includes cable entry facilities through which the cables to be spliced are routed. A support member extends from the cable entry facilities and has a free end disposed adjacent to the closed end of the cover. The support member includes a support base for supporting an optical fiber breakout and a plurality of optical fiber splice trays. On each tray is at least one organizing module which is capable of holding a plurality of optical fiber splices. Each module is capable of holding any of a plurality of splice types, such as fusion, and cleave, sleeve and leave splices. Additional modules may be added as needed. This and similar arrangements have enhanced storage capacity, which is ideal for high density applications. However, such an arrangement is larger than desired and supplies more storage capacity than is needed for low density applications such as fiber-in-the-loop (FITL) and other low density distribution and drop cables.
In most of the prior art arrangements, the emphasis is on adequate storage capacity and fiber protection, with space and ease of access being a secondary consideration. Although some of the foregoing patents, such as the Cobb et al. patent, make size, access, and cost important considerations, for some situations, such as CATV applications, still greater reductions in size, simplicity, and cost are needed.